As a three-dimensional image display system, for which no dedicated glasses or the like are required, a system is known in which a light beam directivity control element is provided on a display panel such as a liquid crystal display or a plasma display. In this system, light beams from the display panel are controlled by the light beam directivity control element so that the light beams reach positions of viewer's eyes. This system is known as a system that can be embodied relatively easily by combining a common display panel with the light beam directivity control element. The light beam directivity control element typically includes a parallax barrier or a lenticular lens and controls light beams so that different images can be viewed depending on the viewing angle direction. This system, however, is disadvantageous in that the resolution of three-dimensional images is lowered and in that the visual quality of two-dimensional images is likely to be lowered. Therefore, directional backlight technologies that control directions of light beams at the backlight are under development.
For example, a known method includes arranging point light sources on a back surface of a light beam directivity control element and changing the direction of directivity at the backlight by switching lighting positions of light sources through time division driving. There is also known a structure in which line light sources are arranged on a back surface of a light beam directivity control element and the arrangement angle of the line light sources are tilted with respect to an edge line direction of the light beam directivity control element. With this structure, different directivities can be provided for respective lines in the column direction of a display panel. A structure in which each line light source is formed by a divided light guide plate is known as an example of the line light source.